Where to get part numbers ?

[JimT]

While I can't prove this, my own experience makes me think that many of these ebay/amazon parts that look identical to OEM parts are either unauthorized production runs by the outsourced asian factories OR they were defective parts rejected by the OEM's QC but someone sold online instead of destroying. I think the latter is more common, but both are known to happen across all industries, especially when they include electronics.

Also, even stingy dealers such as Peterbilt WILL give out part numbers in you specifically ask for them. However if you don't buy at least some stuff from them they aren't going to be as willing to spend their time helping you with anything.